The invention relates to novel alkoxylation products containing lateral hydroxyl groups or bearing lateral C—C double bonds or corresponding polyethers and a process for preparing them by means of an alkoxylation reaction using double metal cyanide (DMC) catalysts.
The novel alkoxylation products containing lateral hydroxyl groups or bearing lateral C—C double bonds in question are, in particular, polyether alcohols, often also referred to as polyethers or polyetherols for short. Polyethers or polyetherols have been known for a long time and are produced in large quantities. They are employed, inter alia, for reaction with polyisocyanates as starting compounds for producing polyurethanes or else for the preparation of surfactants.
It is noted that citation or identification of any document in this application is not an admission that such document is available as prior art to the present invention.
Typically, a hydroxy-functional starter such as butanol, allyl alcohol, propylene glycol or glycerol is reacted in the presence of a suitable catalyst with alkylene oxides such as ethylene oxide, propylene oxide or butylene oxide in an alkoxylation reaction to give an alkoxylation product or polyether. Most processes for preparing such alkoxylation products employ basic catalysts such as alkali metal hydroxides and/or alkali metal methoxides. The use of KOH is particularly widespread. However, it is not always possible to use alkaline catalysis, e.g. in the presence of base-labile functional groups in the starting materials. Thus, for example, the alkoxylation of epihalohydrins using alkali metal hydroxides or alkali metal methoxides is not practicable.
Processes for acid catalysis using HBF4 and Lewis acids such as BF3, AlCl3 and SnCl4 in the alkoxylation have therefore been developed; as described, for example, in DE 10 2004 007 561 (US 2007/0185353). A disadvantage of the acid-catalysed polyether synthesis is the lack of regioselectivity in the ring opening of unsymmetrical oxiranes such as propylene oxide and epichlorohydrin, which leads to polyoxyalkylene chains having some secondary and primary OH end groups being obtained in an uncontrollable manner. The achievable molar masses of the polyethers are also relatively low compared to other catalysts as a result of chain terminations and secondary reactions.
Double metal cyanide (DMC) catalysts have been increasingly used in recent years as catalysts for preparing polyethers. The DMC-catalysed alkoxylation proceeds very selectively and rapidly and allows the preparation of polyethers having high molar masses and a comparatively low polydispersity The preparation and use of double metal cyanide complexes as alkoxylation catalysts has been known since the 1960s and is disclosed, for example, in U.S. Pat. Nos. 3,427,256 , 3,427,334, 3,427,335, 3,278,457, 3,278,458, 3,278,459. Among the evermore effective types of DMC catalysts developed in subsequent years and described, for example, in U.S. Pat. Nos. 5,470,813 and 5,482,908 are, in particular, zinc-cobalt hexacyano complexes. Thanks to their extraordinarily high activity, only low catalyst concentrations are required for the preparation of polyethers.
Polyethers prepared from an OH-functional starter are widespread. The polyethers obtained therefrom have terminal OH groups. Thus, for example, polyethers having one, two or three hydroxyl groups along the chain are formed when using butanol, hexanediol or glycerol. The OH functionality of the polyether, which results automatically from the number of OH groups of the starter, is an important property feature which determines the possible uses of each polyether. Polyethers which are to be crosslinked by means of isocyanates in the synthesis of polyurethanes usually have two, three or more terminal OH functions. The OH functionality determines the crosslinking density and thus decisively determines the materials properties of the final crosslinked material.
In polyethers which are used as nonionic surfactants and emulsifiers, the OH groups act as strongly hydrophilic structural units. They usually form the chain end of polyethers which are obtained by addition of, for example, ethylene oxide on to fatty alcohols. The number and arrangement of the hydroxyl groups in the molecule very critically determines the hydrophile-lipophilie balance in the case of surface-active substances.
The industrially practicable possibilities for obtaining polyethers having a high OH functionality, in particular those having high molecular weights, are limited. Alkoxylation products or polyethers have molar mass distributions. When average molar masses are referred to below, these are the mass averages Mw. Thus, the synthesis of polyethers having four, six or more OH end groups starts out from starters such as pentaerythritol, sorbitol, dipentaerythritol or, for example, sugars or sugar alcohols, which, owing to their high melting points and their poor solubilities in inert solvents are difficult to alkoxylate.
Various documents describe preparing polyhydroxylated polyethers by use of glycidol, glyceryl carbonate and hydroxyoxetanes as monomers or comonomers in addition to other alkylene oxides. In all these processes, branched polyether structures are formed. Such products are frequently referred to as hyperbranched or dendritic polyethers. The incorporation of glycidol, glyceryl carbonate (after elimination of CO2) and hydroxyoxetanes leads, after ring opening, to formation of an additional OH group on which new OH-terminated polyether side chains grow as further monomer is supplied. Each molecule of glycidol, glyceryl carbonate and hydroxyoxetane incorporated into the monomer thus automatically represents a branching point However, the OH-functional monomers at the same time function as chain starters for the monomers subsequently added, so that the end products are complex mixtures of polyethers which have different branching and a broad molar mass distribution. The OH functions are always present on the end groups of the main and side chains but never laterally in the middle of such a chain.
The (co)polymerization of glycidol under alkali-catalysed conditions to form highly branched polyetherols for polyurethane applications is described, for example, in WO 2000/037532. The preparation of polyhydroxylated polyethers having a dendritic structure from ethylene oxide, propylene oxide and glycidol is described by Feng et al. in Macromolecules (2009), 42 (19), 7292-7298. In J. Appl. Polym. Sci. (2001), 82(9), 2290-2299 Royappa et al. studied the cationic copolymerization of glycidol with various other epoxy compounds to form hyperbranched amphiphilic polyethers. EP 0 116 978 describes branched polyetherols having linear structural segments generated by KOH-catalysed reaction of polyethylene glycol with glycidol and ethylene oxide. EP 1 249 464 (US 2002/0182469) describes polyethers which are based on ethylene oxide and glycidol and have structural elements of the type [—CH2—CH(CH2O—)—O—] in addition to ethylenoxy units. The description and the examples indicate that this structural feature represents a branching point in the polyether skeleton and the products are thus hyperbranched polymers in which the lateral function is again a starting point for further alkoxylation steps or else bears an alkyl group.
DE 10 2008 032066 (US 2011/0185947) highlights poly-OH-functional allyl polyethers obtained by alkali-catalysed alkoxylation of glycidol or glyceryl carbonate with other alkylene oxides. The unsaturated polyethers which can be obtained in this way are reacted with hydrogensiloxanes in a hydrosilylation reaction to form highly OH-functional polysiloxane-polyether copolymers which have an antiadhesive, dirt-repelling action in coatings.
With regard to storage stability and toxicology, the use of hydroxy-functional oxetanes as monomers for generating OH groups and at the same time branching points has a significant advantage over glycidol. Thus, U.S. Pat. No. 7,176,264 describes a process for preparing dendritic polymers based on 3-ethyl-3-hydroxymethyloxetane. DE 10 2006 031 152 discloses branched polyhydroxy-functional allyl polyethers obtained by use of hydroxyoxetane in an alkoxylation reaction. Such copolymers with hydrogensiloxanes are employed in polar, usually aqueous surface coating systems.
Halogen-substituted polyethers obtained using DMC catalysts and epihalohydrins are known from U.S. Pat. No. 7,423,112. The halogenated polyethers described therein are converted into amine-functional polyethers in a further substitution reaction with amines.
Only few chemical processes which allow additional OH groups to be generated laterally and not only terminally in a polyether chain and thus avoid the formation of branched polymer structures have hitherto been described. Thus, U.S. Pat. No. 3,578,719 described polyhydroxylated surfactants for cosmetic applications which are obtained in a two-stage process from fatty alcohol starters having 8-22 carbon atoms by 1-10 mol of epichlorohydrin firstly being added on in an acid-catalysed alkoxylation reaction before, in the second step, the organically bound chlorine is converted into lateral OH groups in a substitution reaction in the presence of alkali metal carboxylates and polar solvents. The short-chain polyethers containing up to ten elements of the type [—CH2—CH(CH2OH)—O—] have an additional terminal OH group based on the monofunctional starter alcohol. BF3, SnCl4 and SbCl5serve as catalyst for the polyaddition of epichlorohydrin. A disadvantage is that only homopolymers of epichlorohydrin and hydroxylated downstream products thereof having low molar masses can be obtained by the abovementioned route. A very large amount, based on the product yield, of alkali metal chloride is formed and, as salt, is difficult to separate off. The formation of the very OH-rich end products requires not only high temperatures of 180° C. but also the use of polar, protic, high-boiling solvents such as dipropylene glycol in order to achieve quantitative elimination of chlorine. The solvent can subsequently be removed by distillation only with difficulty because of its high boiling point. In addition, it can be only partly recycled since it is partly esterified.
GB 1267259 and GB 1516195 describe the preparation of polyethers having [—CH2—CH(CH2OH)—O—] structural units as cosmetic oils by the use of tert-butyl glycidyl ether as monomer in a base-catalysed or Lewis acid-catalysed alkoxylation reaction. The process allows up to ten units of tort-butyl glycidyl ether to be added on in a block-like fashion per OH group of the starter alcohol. The tert-butyl groups are subsequently split off in the form of isobutylene in the presence of strong acids and the hydroxyl groups are thus formed. Chemically, tert-butyl glycidyl ether is an etherified glycidol. Since the OH group is protected, undesirable chain branches in the polymer structure are prevented. Likewise, the protected glycidol cannot function as chain starter because of the lack of an OH function. A disadvantage of the process is the restriction imposed by the unselective catalysis to products having relatively low molar masses and to structures having not more than ten [—CH2—CH(CH2OH)—O—] units, which are, in addition, exclusively bound in a block-like fashion.
Apart from the hydroxy functionalization, the functionalization by unsaturated groups plays an important role. A person skilled in the art will know of numerous methods of integrating C—C double bonds into polyethers. Polyethers which bear allyl groups and can be prepared, for example, from allyl alcohol, glyceryl monoallyl or diallyl ether or, for example, pentaerythritol monoallyl, diallyl or triallyl ether by a subsequent alkoxylation reaction are particularly widespread. The use of allyl glycidyl ether as monomer in the alkoxylation reaction is likewise known. Further structures bear alkenyl groups and are obtained, for example, by alkoxylation of vinyl oxyalcohols or unsaturated alcohols such as hexenol. Acrylate- and methacrylate-functionalized polyethers are also known and can be prepared, for example, by esterification of OH-functional polyethers with the respective unsaturated acid or by use of glycidyl (meth)acrylate as monomer in the alkoxylation.
The possible uses of unsaturated alkoxylation products such as polyethers are very versatile because of their reactivity and likewise known to those skilled in the art. Apart from the formation of polyether siloxanes by means of a hydrosilylation reaction, free-radical, ionic or radiation-induced curing plays an important role.
There is a lack of a process which allows both polyethers having multiple hydroxy functionality and those having unsaturated groups to be prepared, with the number of hydroxyl groups formed and the unsaturated groups in the molecule being able to be controlled by simple variation of the process conditions.
There is also a lack of hydroxy-functional alkoxylation products or polyethers which are neither dendritic nor hyperbranched in nature but whose structure is characterized by linear polyoxyalkylene chains having [—CH2—CH(CH2OH)—O—] units which are, as desired, incorporated randomly or in blocks and also of a process which allows such hydroxylated compounds to be prepared economically and reproducibly, with high molar masses and in a great structural variety, without the secondary and chain termination reactions known from acid or alkaline catalysis occurring in the alkoxylation. There is also a lack of unsaturated polyethers which bear units of the type [—CH2—(═CH2)—O—] which are distributed, as desired, either randomly or in blocks in the molecular chain, and also of a process for preparing them. There is also a lack of polyethers which bear both OH-functional [—CH2—CH(CH2OH)—O—] units and unsaturated vinyl ether units of the type [—CH2—C(═CH2)—O—] in the same molecular chain, and also of a process which enables such doubly functionalized alkoxylation products to be prepared in a simple, reproducible way.
It is noted that in this disclosure and particularly in the claims and/or paragraphs, terms such as “comprises”, “comprised”, “comprising” and the like can have the meaning attributed to it in U.S. Patent law; e.g., they can mean “includes”, “included”, “including”, and the like; and that terms such as “consisting essentially of” and “consists essentially of” have the meaning ascribed to them in US. Patent law, e.g., they allow for elements not explicitly recited, but exclude elements that are found in the prior art or that affect a basic or novel characteristic of the invention.
It is further noted that the invention does not intend to encompass within the scope of the invention any previously disclosed product, process of making the product or method of using the product, which meets the written description and enablement requirements of the USPTO (35 U.S.C. 112, first paragraph) or the EPO (Article 83 of the EPC), such that applicant(s) reserve the right to disclaim, and hereby disclose a disclaimer of, any previously described product, method of making the product, or process of using the product